Polymers containing free hydroxyl groups are well-known to the art, and are useful for a variety of purposes. For example, polymers such as poly(vinyl alcohol) and poly(hydroxyethyl methacrylate) are well known. Some polymers containing hydroxyl groups, such as poly(vinyl alcohol) form excellent hydrogels, i.e., they absorb large amounts of water without dissolving. Hydrogels have desirable physical, optical, and physiological properties and are useful, for example, as contact lens materials. However, in order to obtain properties of strength and structural integrity, these polymers are generally cross-linked. See, for example, U.S. Pat. Nos. 3,220,960 and 3,361,858. It is known in the art that the strength of these polymers is generally related to the amount of cross-linking present.
It is also well-known that hydroxyl-containing polymers, due to extensive hydrogen bonding interactions, are generally not moldable into shapes with structural integrity, that such polymers are generally considered infusible and non-thermoplastic, and that they undergo thermal degradation before temperatures allowing melt-flow (i.e., melting without degradation) are attained. Furthermore, cross-linked polymeric materials are generally not moldable into shaped articles since covalent bonds between polymer molecules do not allow unrestricted flow of polymers even at elevated temperatures. When the amount of cross-linking is extremely low, cross-linked polymers can sometimes be formed into films or other thin shapes, e.g., by solvent casting. It is recognized in the art that when the cross-linking in hydrogels is minimal, the strength is reduced.
In order to provide shaped articles having hydrogel properties from hydroxyl-containing monomers, the articles also possessing adequate strength and structural integrity, two processes are used in the art. One process requires forming a cross-linked polymer, cutting and machining the cross-linked polymer into the desired shape and configuration and then hydrating the article to provide a hydrogel article. This process utilizes labor-intensive cutting, machining, polishing, and the like. The other process, called spin casting is described, for example, in U.S. Pat. No. 3,408,429 and requires that polymerization in the presence of a crosslinking agent be carried out in a rotating mold which approximates the shape of the desired article. After polymerization the article is further processed if necessary to attain the final shape. The shaped article is then hydrated to provide a hydrogel article.
An early attempt to hydrolyze vinyl trifluoroacetate polymers is disclosed in U.S. Pat. No. 2,436,144 (see Example VIII). It is taught in the patent that the polymer obtained by hydrolysis is soluble in water, i.e., it is not a hydrogel. The polymers of polyvinyl trifluoroacetate obtained are described as colorless, transparent, tough and thermoplastic (col. 3, 11. 25-31). Further, the patent discloses molded articles of polyvinyl trifluoroacetate having softening temperatures of 70.degree. C. Thus, the poly(vinyl trifluoroacetate) and its hydrolysis product of this patent are significantly different from that of the present invention.
Poly(vinyl trifluoroacetate) has also been hydrolyzed by other workers to poly(vinyl alcohol) in studies of the stereoregularity of poly(vinyl alcohol), e.g., Harris, et al., J. Polymer Sci., Part A-1, 4, 649-677 (1966) and Pritchard, et al., J. Polymer Sci., Part A-1, 4, 707-712 (1966). These authors did not preform the poly(vinyl trifluoroacetate) into shaped articles nor recognize the possibility or significance of doing so.
U.S. Pat. No. 3,470,124 describes monomers of the formula R'COO--Y--OOCR", wherein R'COO is a perfluoroalkanoic acid residue; R"COO is a residue of a polymerizable alkenoic acid; and Y is a residue of an organic compound selected from the group consisting of aliphatic, aliphatic-aromatic and aromatic dihydric alcohols as well as the functional derivatives thereof. The reference relates to maximizing the properties of the monomers and polymers obtained by incorporating fluorine into the acyl group in the materials. Thus, trifluoroacetoxyethyl methacrylate was not prepared, nor was its potential as a source of either poly(trifluoroacetoxyethyl methacrylate) or poly(hydroxyethyl methacrylate) appreciated.
Cross-linked and uncross-linked poly(vinyl alcohol) is known in the art. The properties of these forms of poly(vinyl alcohol) are known to differ as is disclosed in J. Polymer Sci., 14, 441-457 (1976). Previous preparations of poly(vinyl alcohol) and shaped articles formed therefrom (see U.S. Pat. No. 3,361,858) do not exhibit the improved properties obtained in the shaped poly(vinyl alcohol) articles of the present invention.